Recently, in the field of endoscope, a swallowable capsule endoscope has been proposed. In this capsule endoscope, an imaging function and a radio communication function are provided. The capsule endoscope has a function of sequentially taking images after the capsule endoscope is swallowed from a mouth of a patient (a human body) for observation (examination) until it is naturally discharged, while passing through body cavities, for example, internal organs such as a stomach and a small intestine, according to the peristalsis thereof.
Image data obtained inside the body by the capsule endoscope while moving inside the body cavities is sequentially transmitted to the outside by radio communication, and stored in a memory externally provided. If the receiver having the radio communication function and the memory function is carried, the subject can freely act during whole period from swallow of the capsule endoscope until discharge thereof. After the capsule endoscope is discharged, doctors and nurses can perform diagnosis based on the image data stored in the memory by displaying an image of the organs on a display (for example, see Patent Document 1).
Furthermore, among conventional capsule endoscope systems, there has been proposed a system provided with a mechanism to detect a position of the capsule endoscope inside a body cavity. For example, a magnetic field of which strength is position dependent is generated inside the body of a subject to which the capsule endoscope is introduced, and based on the strength of the magnetic field that is detected by a magnetic field sensor provided in the capsule endoscope, position of the capsule endoscope inside the body of the subject can be detected. In the capsule endoscope system, such a configuration is adopted that a predetermined coil is arranged to generate the magnetic field, and by feeding a predetermined electric current to this coil, the magnetic field is generated inside the body of the subject. In this case, because it is difficult to detect a position of the capsule endoscope in advance, the magnetic field to be generated should be strong enough to enable detection by the capsule endoscope in all areas in which the capsule endoscope is possible to be positioned inside the body of the subject. Specifically, in the conventional capsule endoscope systems, the magnetic field with which detection by the capsule endoscope can be achieved in all digestive organs from the buccal cavity to the anus is generated.    Patent Document 1: Japanese Patent Application Laid-open No. 2003-19111